Representing Audio

Question 1

Transducer refers to what?

Answer 1

microphone

Question 2

A Transducer converts sound waves to what?

Answer 2

electrical signals

Question 3

Is a sound signal analog or digital data?

Answer 3

Analog

Question 4

What are the 2 ways of creating digital audio?

Answer 4

1. Sampling
2. Synthesis

Question 5

What is sampling?

Answer 5

Analog data to digital data

Question 6

What is synthesis?

Answer 6

to create artificial sound through computers

Question 7

In the sine wave equation:
What does the “a” represent?

Answer 7

amplitude, related to intensity

Question 8

In the sine wave equation:
What does the “f” represent?

Answer 8

frequency, related to perceived pitch

Question 9

In the sine wave equation:
What does the “O” represent?

Answer 9

phase, can depend on the location of the sound

Question 10

What does the period of the sine wave mean?

Answer 10

How long does it take to repeat once

Question 11

Period is equal to what?

Answer 11

1/frequency

Question 12

We can only hear frequencies at what Hz?

Answer 12

16-20 Hz

Question 13

Sampling frequency is equal to what?

Answer 13

equal to or greater than 2 times the frequency

Question 14

What does Higher bit depth give us?

Answer 14

• more data
• more accurate samples
• takes up more space

Question 15

A bit depth of less than 8 is used for what?

Answer 15

• not used for sound
• can be used to record blood pressure, heart rate

Question 16

A bit depth of 8 is used for what?

Answer 16

• Common in telephony
• Quantization of noise sometimes

Question 17

A bit depth of 16 is used for what?

Answer 17

• highest quality sound
• CDS, DAT, MP3, movies, audio tracks

Question 18

A bit depth of 24 is used for what?

Answer 18

• even higher quality than 16-bit
• often used before and after sound processing/editing
• DVD, Audio, DTS

Question 19

What is the equation for bit rate?

Answer 19

(sampling rate)(bit depth)(channels)

Question 20

An uncompressed audio will typically be saved as what?

Answer 20

.wav format

Question 21

How many channels are we using?

Answer 21

Either 1 or 2

Question 22

When was digital audio developed?

Answer 22

70s

Question 23

When were CDS released?

Answer 23

1982

Question 24

What is the CD capacity?

Answer 24

74 mins audio format, 780 MB

Question 25

What is the only practical way to store a massive amount of data?

Answer 25

video tape

Question 26

What are the 2 techniques for audio compression?

Answer 26

1. Lossless
2. Lossy

Question 27

What are the 2 substeps of what Lossy compression will do?

Answer 27

1. Remove imperceptible sound
2. Reduces bit rate

Question 28

How does lossy compression remove imperceptible sound?

Answer 28

via psychoacoustics models
- It will remove sounds that are at frequencies we cannot hear anyway

Question 29

How does lossy compression reduce bit rate?

Answer 29

using codecs, compression and decompression algorithms for audio and video

Question 30

What is a consequence of lossy compression reducing the bit rate?

Answer 30

• less accurate reproduction of the original

Question 31

What are 3 examples of Codecs?

Answer 31

1. FLAC
2. MP3
3. AAC

Question 32

What is FLAC?

Answer 32

• Lossless
• using a combination of linear predictive coding and a technique similar to Huffman’s encoding called Rice coding

Question 33

What is MP3?

Answer 33

• Lossy
• uses psychoacoustics, Huffman’s encoding and lower bit rates
• popular on most devices

Question 34

What is ACC?

Answer 34

• Lossy
• uses psychoacoustics, Huffman’s encoding and lower bit rates
• better perceived quality than MP3
• Popular on Apple devices and most modern smartphones

Question 35

What is the compression ratio for MP3?

Answer 35

13%

Question 36

What is the compression ratio for ACC?

Answer 36

14%

Question 37

What is the compression ratio for FLAC?

Answer 37

62%

Question 38

Out of FLAC, MP3 and ACC, which are lossless and which are lossy?

Answer 38

lossy: MP3, ACC
lossless: FLAC